It’s unclear if any deal is finalized, or how much money might be involved. But the main scientist behind the effort, Nobel Prize–winning Stanford physics professor Robert Laughlin, revealed that a deal was in the works in the abstract of a talk at Stanford scheduled for late last month.

In the abstract, he mentions the “secret project at X code named ‘Project Malta,’” notes that a “key patent” for the molten-salt technology was issued in early April, and adds: “Spinoff activity associated with Bill Gates’s Breakthrough Energy Ventures is presently underway.”

The page was taken down after inquiries from MIT Technology Review.

Laughlin referred the publication to Breakthrough Energy Ventures, which didn’t respond to questions before press time. A spokesperson for X declined to comment.

In another notable connection, Phil Larochelle, who worked with Laughlin on an earlier thermal storage venture and co-holds several of the relevant patents, is now an investment principal at Breakthrough Energy Ventures. Larochelle, who also served as a senior technical program manager in the X division, didn’t reply to an inquiry.

Project Malta was revealed in a Bloomberg story last July, which said the team was “looking for partners to build, operate and connect a commercial-sized prototype to the grid.”

The proposed system converts electricity from solar and wind turbines into thermal energy, resulting in heat that is stored in giant tanks of molten salt and cold that is stored in vats of liquid coolant. The approach could achieve higher efficiencies and lower costs than earlier thermal storage systems through the use of a heat engine that transfers “heat from the hot side to the cold side to mechanically drive the turbine,” according to the April patent and additional explanation in a scientific paper Laughlin published on the technology.

The researchers believe the approach will allow them to store energy for longer than is possible with lithium-ion batteries at prices competitive with pumped hydroelectric, the cheapest large-scale form of storage today, Bloomberg reported.

Cheaper and better forms of grid storage are considered essential to handle fluctuating renewable sources like wind and solar as they start to contribute a greater portion of total electricity supplies.

That’s precisely why grid storage is one of five focus areas for Breakthrough Energy Ventures, which launched in 2016 to support the cutting-edge energy technologies necessary to confront climate change. Other prominent investors involved in the fund include John Doerr of Kleiner Perkins, Jack Ma of Alibaba Group, and Salesforce chief executive Marc Benioff. Breakthrough’s other investment areas include liquid fuels, microgrids, alternative building materials, and geothermal energy.